That's a pretty solid machine. I can give you my perspective if that helps. I have a 2.5Ghz i5, 8GB of RAM with a SSD. I plan to get at least another three years out of that. Now, Apple may eventually phase out your machine but until then, I'd say you can keep yours.

Well, your machine is three years old so at some point in the next few years, Apple will stop supporting that hardware. According to Wikipedia, these are the system requirements for Mavericks (for example):